1. Field of the Invention
The present invention relates to hand-propelled wheelchairs.
More particularly the present invention relates to improved wheelchairs enabling the variance of the center of gravity of the user and the seat of the wheelchair with reference to the axis of the drive wheels.
2. Description of the Related Art
In the last decade many patents have issued which propose various ways to change or alter the overall center of gravity of the wheelchair for different purposes.
Thus, e.g. U.S. Pat. No. 4,310,167 describes and claims a variable position center of gravity wheelchair comprising an articulated chassis having a subframe to which is mounted a pair of main wheels and a rear caster wheel, and a seat frame assembly carrying a seat and a front caster wheel and connected to the subframe for movement relative thereto between a first position with the seat positioned over the main wheels and a second position forwardly of the main wheels to facilitate curb climbing; said main wheels and front and rear caster wheels being arranged in a diamond pattern whereby lateral drift of the wheelchair is minimized while traversing sloping surfaces; and resiliently yieldable means connected between the subframe and seat frame assembly to minimize the tendency for the front caster wheel to lift off the ground when the main wheels are strongly propelled, and to provide shock absorption when traversing rough ground.
As stated in said above noted Patent, the principal object thereof was the design of a wheelchair which can traverse sloping surfaces without experiencing side drift and yet which may be easily manipulated to climb curbs and the like and which may traverse rough ground without undue discomfort to the user.
A still further object of said patent was to provide a movable center of gravity wheelchair in which the seat and thus the center of gravity is located essentially over the main wheels during normal use but in which means is provided for easily shifting the seat and center of gravity forwardly to remove weight from the main wheels to facilitate curb climbing.
The disadvantage of said arrangement is that it is limited to articulated movement of a subframe comprising the seat and front caster wheel from a first position to a second position for curb climbing.
In a series of Patents by J. P. Minnebraker there is described a different type of wheelchair construction enabling the use of the same wheelchair for normal riding conditions and in sports activities.
Thus, as described in U.S. Pat. Nos. 4,351,540 and 4,477,098 and in U.S. Pat. No. Re. 32,242 wheelchair constructions have remained unchanged, except for relatively minor features for a substantial period of time. While wheelchairs have existed for many years, they generally were constructed of a main frame, front and rear wheels, side rails or so-called "arm rests" and foot support members. However, there was no means for creating or manufacturing a wheelchair of different sizes, at a relatively low cost, from standard sized components, in order to accommodate different size users.
Prior art wheelchair manufacturers constructed several different sized wheelchairs and used different sized components for each of the differently sized wheelchairs. In the case of a tall individual, the main frame had to be larger, the seat located in a different position, and a foot support member extended further from the seat, than in the case of a wheelchair for a smaller individual. In addition, for the larger sized wheelchair, the seat may have to be located at a higher elevation in order to permit the user to engage rims on the wheels for propelling the wheelchair in an easy and convenient manner.
Notwithstanding, heretofore there has not been any wheelchair which is designed for anything except normal transport. In other words, wheelchairs heretofore constructed were not designed to permit any form of athletic activity, and particularly, for fast-moving sports activities. This was primarily due to the fact that the prior art wheelchairs were all of a box-like construction with the seat, and hence, the center of gravity, located at a fixed and at a substantial distance above the ground. Consequently, the prior art wheelchairs were not designed for any fast movement, and if one attempted to propel any of the prior art wheelchairs at any significant speed, or attempted to turn a corner quickly,the wheelchair might well tip over, causing injury to the user.
In recent years, it has been found to be highly beneficial for paraplegics and others required to use wheelchairs on a relatively permanent basis to engage in various forms of athletic activities, including wheelchair racing, tennis and the like. However, the wheelchair construction heretofore did not lend themselves to such form of activities.
In the wheelchairs described in each of said Patents and especially in U.S. Pat. No. Re. 32,242 there is described and claimed an apparatus for selectively positioning the rear wheels of a wheelchair having a frame means to selectively alter the center of gravity thereof, said apparatus comprising:
a. a first pair of connected and spaced apart plates provided for attachment to one side of said frame means and a second pair of connected and spaced apart plates provided for attachment to an opposite side of said frame means. PA1 b. a plurality of axle receiving openings on each of said pairs of spaced apart plates and the openings in the plates of each pair being aligned so as to be capable of receiving a rear wheel axle in each of said axle receiving openings, PA1 c. a separate rear wheel axle capable of extending outwardly from the rear wheel axle openings on each of said pairs of plates, PA1 d. flange means on at least one of the plates of each of said pairs for fastener attachment to a frame means of said wheelchair such that the pairs of plates can be attached to the frame means in any of a plurality of selected locations to accommodate the size and intended use of a user. PA1 e. quick release means associated with said rear wheel axle to enable quick release and replacement of rear wheels on said rear wheel axle, such that said axle can be easily removed from one location and replaced in another axle receiving location on said plates so that the response and center of gravity and wheel base on said frame can be easily and quickly altered.
Thus, Minnebraker's approach to providing a multifunctional wheelchair which would be used for normal indoor and outdoor use as well as for sports activities was based on providing the frame with a plurality of axle receiving openings so that the center of gravity of the wheelchair could be altered by disassembling the wheelchair and repositioning the wheels relative to the frame.
In U.S. Pat. No. 4,405,142 there is described and claimed a similar arrangement of a quick breakdown wheelchair assembly comprising a pair of side frames wherein each of said side frames includes a wheel bracket for detachably mounting a wheel, said wheel bracket having a plurality of axle mounting bores.
While this approach has been adopted on wheelchairs marketed today, it has many disadvantages as discussed fully in U.S. Pat. No. 4,852,899 which points out that with the growing participation of wheelchairs in sports, greatly increased demands have been placed upon the balance and as well the general maneuverability of a wheelchair. In this regard decisive meaning has been attached to the maneuvering speed of the so-called sportschairs, in particular with the basketball wheelchairs.
Modification of the center of gravity of a chair raises or lowers the maneuvering speed of these chairs. However, on the one hand it should not be forgotten that each modification of the center of gravity naturally changes and affects the stability and/or tipping possibilities of the device with increasing degree.
Further, it is generally recognized that the more a person moves the axles for the two load bearing rear wheels rearwardly, that is, displacement in the direction opposite from the two front wheels of the wheelchair, the more stabilization is gained for the wheelchair as such. On the other hand, with such adjustment the front part of the wheelchair becomes heavier and heavier, as is apparent from its own weight, and with this, naturally, comes decreased maneuverability.
Besides the individual possibilities of shifting the center of gravity, there is also the need to take into consideration for today's state of the art the various adjusting possibilities for the angle of the seat, the angle of the backrest in regard to the seat surface as well as the adjustment possibility of the camber of the rear wheels in order to shift the height of the center of gravity.
For adjusting the center of gravity in relation to the seat surface one can make use of essentially two adjustment criteria in the state of the art. For structural solution to the shifting of the center of gravity below the seat surface of a wheelchair, one utilizes a rearrangement of the two large drive wheels of the wheelchair. These two drive wheels are for the most part repositionable back and forth along their axes in longitudinal guides of the so-called axial support plates. By these means, the wheels themselves can be adjusted in a direction closer to or further from the smaller front wheels.
For angular adjustment of the seat back of the wheelchair with response to the seat surface, the so-called "positioning angle" has been primarily employed in the prior art. By these means the seat back is adjusted for each application and then is fixedly locked in the adjustment position by means of this positioning angle.
In addition, in the prior art, the two front wheels are not directly connected with the frame bars of the seat surface, but instead they are pivotally connected to this frame so that they work as carrying bars which extend parallel to the seat surface frame bars. In this regard, they are also angularly adjustable as is illustrated for example on page 15 of the publication mentioned immediately above.
It has also been established in the prior art to be a serious disadvantage first that precise adjustment of the three interrelated adjustment parameters with respect to one another, these being the position of the axles of the rear wheels, the position of the vertical axles of the front wheels and the angle between the seat surface and the back rest, is achieved only with great difficulty. For this the two rear wheels in certain constructions are always individually adjustable, that is, the axles of each individual wheel are separately and distinctly adjusted. It is therefore not difficult to demonstrate how easily a small change in the setting of one wheel axis can affect the other two wheel axes. Now this however, leads to a skewing of the actual wheel axis relative to the seat surface of the wheelchair, and with it a disadvantageous modification of the balance and also, quite substantially, the tracking of the wheelchair. Still more severely dominant, however, is the shifting which thereby occurs such that the fixing means of one wheel becomes dissociated from the other wheel and introduces the possibility of a completely unexpected shifting of one wheel axis with respect to the opposing wheel axis.
Furthermore, tools are required to effect a positional change, so in practice the position chosen is usually retained without change.
To overcome the above problem U.S. Pat. No. 4,852,899 suggests that by adjusting two telescoping-type interengaging shiftable parts for each of two frame bars of a support frame of a lightweight wheelchair, the sitting position of the same can be adjusted with respect to the seat surface and with it the adjustment of the center of gravity can be dynamically adjusted with respect to the user.
Thus, said patent provides a lightweight wheelchair adjustable for a specific balance, comprising a seat arranged on two frame bars characterized in that the frame bars at the seat level have at least two parts telescopically adjustable relative to one another and adjustably connecting the back rest with the support frame to selectively shift the position of the back rest relative to the seat.
It is not possible to effect a positional change while the user occupies the seat of the wheelchair.
This arrangement has the disadvantage that the center of gravity is shifted by forcing the user to sit further back or further forward in the seat as a function of the positioning of the backrest which is a source of discomfort to the user.
In U.S. Pat. No. 4,489,955 there is also cognizance of the disadvantage of providing a wheel bracket having a plurality of axle mounting bores for repositioning of the wheels relative to the frame to adjust and vary the center of gravity and thus said patent suggests yet another approach to this problem.
Thus said patent inter alia describes and claims a wheelchair comprising a base frame comprising a pair of side plates and a web extending between said side plates; a plurality of wheels including two drive wheels and at least one other wheel; means for propelling said drive wheels, said means consisting of hand engagable rim means associated with said drive wheels; means for mounting said wheels to said base frame, but so that the wheelbase thereof is substantially fixed; chair support means; and means for mounting said chair support means to said frame so that the position of said chair support means with respect to said frame and with respect to said drive wheels is adjustable, so that the center of gravity of said wheelchair is adjustable by adjusting the portion of said chair support means with respect to said frame, and without adjustment of the position of said drive wheels with respect to said frame, said means comprising: a pair of inner and outer flanges of said chair means for receipt of each of said frame side plates; means defining elongated openings in said web adjacent each of said side plates; and fastener means extending through said elongated openings into operative association with said chair support means.
As will be realized said patent also has the same disadvantage as the means suggested by Minnebraker in that the center of gravity for any specific use must be prechosen and fixed before the user mounts the chair thereby increasing the dependency of the user on others and failing to provide dynamic versatility.